Merge node

This documentation is for version 2.0 of Merge (net.sf.openfx.MergePlugin).

Description

Pixel-by-pixel merge operation between two or more inputs. Input A is first merged with B (or with a black and transparent background if B is not connected), then A2, if connected, is merged with the intermediary result, then A3, etc.

A description of most operators is available in the W3C Compositing and Blending Level 1 Recommendation https://www.w3.org/TR/compositing-1/ and a complete explanation of the Porter-Duff compositing operators can be found in “Compositing Digital Images”, by T. Porter and T. Duff (Proc. SIGGRAPH 1984) http://keithp.com/~keithp/porterduff/p253-porter.pdf

Note that if an input with only RGB components is connected to A or B, its alpha channel is considered to be opaque (one) by default, thus the output will be completely opaque if the checkbox for channel A of input B is checked. One reason for this behaviour is that non-zero RGB values with a zero A value are not valid alpha-premultiplied RGBA values. If the user wishes to keep the background fully transparent, it can only be black, which is equivalent to not using the merge operator. Non-black fully transparent pixels should never appear anywhere in a proper compositing graph.

Operators

The following operators are available.

Porter-Duff compositing operators

• copy: A (a.k.a. src)

• over: A+B(1-a) (a.k.a. src-over)

• under: A(1-b)+B (a.k.a. dst-over)

• in: Ab (a.k.a. src-in)

• mask: Ba (a.k.a dst-in)

• out: A(1-b) (a.k.a. src-out)

• stencil: B(1-a) (a.k.a. dst-out)

• atop: Ab + B(1 - a) (a.k.a. src-atop)

• xor: A(1-b)+B(1-a)

Blend modes, see https://en.wikipedia.org/wiki/Blend_modes

Multiply and Screen

• multiply: AB, A if A < 0 and B < 0

• screen: A+B-AB if A or B <= 1, otherwise max(A, B)

• overlay: multiply(A, 2*B) if B < 0.5, screen(A, 2*B - 1) if B > 0.5

• hard-light: multiply(2*A, B) if A < 0.5, screen(2*A - 1, B) if A > 0.5

• soft-light: burn-in if A < 0.5, lighten if A > 0.5

Dodge and burn

• color-dodge: brighten B towards A

• color-burn: darken B towards A

• pinlight: if B >= 0.5 then max(A, 2*B - 1), min(A, B * 2) else

• difference: abs(A-B) (a.k.a. absminus)

• exclusion: A+B-2AB

• divide: A/B, 0 if A < 0 and B < 0

Simple arithmetic blend modes

• divide: A/B, 0 if A < 0 and B < 0

• plus: A+B (a.k.a. add)

• from: B-A (a.k.a. subtract)

• minus: A-B

• difference: abs(A-B) (a.k.a. absminus)

• min: min(A, B) (a.k.a. darken only)

• max: max(A, B) (a.k.a. lighten only)

Hue, saturation and luminosity

• hue: SetLum(SetSat(A, Sat(B)), Lum(B))

• saturation: SetLum(SetSat(B, Sat(A)), Lum(B))

• color: SetLum(A, Lum(B))

• luminosity: SetLum(B, Lum(A))

Other

• average: (A + B) / 2

• conjoint-over: A + B(1-a)/b, A if a > b

• disjoint-over: A+B(1-a)/b, A+B if a+b < 1

• freeze: 1-sqrt(1-A)/B

• geometric: 2AB/(A+B)

• grain-extract: B - A + 0.5

• grain-merge: B + A - 0.5

• hypot: sqrt(A*A+B*B)

• matte: Aa + B(1-a) (unpremultiplied over)

• reflect: A*A / (1 - B)

See also:

• “Digital Image Compositing” by Marc Levoy https://graphics.stanford.edu/courses/cs248-06/comp/comp.html

• “Compositing and Blending Level 1” https://www.w3.org/TR/compositing-1/

• “SVG Compositing Specification” https://www.w3.org/TR/SVGCompositing/

• “ISO 32000-1:2008: Portable Document Format (July 2008)”, Sec. 11.3 “Basic Compositing Operations” http://www.adobe.com/devnet/pdf/pdf_reference.html

• “Merge” by Martin Constable https://web.archive.org/web/20220627015903/http://www.opticalenquiry.com/nuke/index.php?title=Merge

• “Merge Blend Modes” by Martin Constable https://web.archive.org/web/20220807185657/http://www.opticalenquiry.com/nuke/index.php?title=Merge_Blend_Modes

• “Primacy of the B Feed” by Martin Constable https://web.archive.org/web/20220807185551/http://www.opticalenquiry.com/nuke/index.php?title=Primacy_of_the_B_Feed

• grain-extract and grain-merge are described in http://docs.gimp.org/en/gimp-concepts-layer-modes.html

Inputs

Input	Description	Optional
B	The main input. This input is passed through when the merge node is disabled.	Yes
A	The image sequence to merge with input B.	Yes
Mask		Yes
A2		Yes

Controls

Parameter / script name	Type	Default	Function
Operation / operation	Choice	over	The operation used to merge the input A and B images. The operator formula is applied to each component: A and B represent the input component (Red, Green, Blue, or Alpha) of each input, and a and b represent the alpha channel of each input. If Alpha masking is checked, the output alpha is computed using a different formula (a+b - a*b). Alpha masking is always enabled for HSL modes (hue, saturation, color, luminosity). atop: Ab + B(1 - a) (a.k.a. src-atop) average: (A + B) / 2 color: SetLum(A, Lum(B)) color-burn: darken B towards A color-dodge: brighten B towards A conjoint-over: A + B(1-a)/b, A if a > b copy: A (a.k.a. src) difference: abs(A-B) (a.k.a. absminus) disjoint-over: A+B(1-a)/b, A+B if a+b < 1 divide: A/B, 0 if A < 0 and B < 0 exclusion: A+B-2AB freeze: 1-sqrt(1-A)/B from: B-A (a.k.a. subtract) geometric: 2AB/(A+B) grain-extract: B - A + 0.5 grain-merge: B + A - 0.5 hard-light: multiply(2*A, B) if A < 0.5, screen(2*A - 1, B) if A > 0.5 hue: SetLum(SetSat(A, Sat(B)), Lum(B)) hypot: sqrt(A*A+B*B) in: Ab (a.k.a. src-in) luminosity: SetLum(B, Lum(A)) mask: Ba (a.k.a dst-in) matte: Aa + B(1-a) (unpremultiplied over) max: max(A, B) (a.k.a. lighten only) min: min(A, B) (a.k.a. darken only) minus: A-B multiply: AB, A if A < 0 and B < 0 out: A(1-b) (a.k.a. src-out) over: A+B(1-a) (a.k.a. src-over) overlay: multiply(A, 2*B) if B < 0.5, screen(A, 2*B - 1) if B > 0.5 pinlight: if B >= 0.5 then max(A, 2*B - 1), min(A, B * 2) else plus: A+B (a.k.a. add) reflect: A*A / (1 - B) saturation: SetLum(SetSat(B, Sat(A)), Lum(B)) screen: A+B-AB if A or B <= 1, otherwise max(A, B) soft-light: burn-in if A < 0.5, lighten if A > 0.5 stencil: B(1-a) (a.k.a. dst-out) under: A(1-b)+B (a.k.a. dst-over) xor: A(1-b)+B(1-a)
Bounding Box / bbox	Choice	Union	What to use to produce the output image’s bounding box. Union (union): Union of all connected inputs. Intersection (intersection): Intersection of all connected inputs. A (a): Bounding box of input A. B (b): Bounding box of input B.
Alpha masking / screenAlpha	Boolean	Off	When enabled, the input images are unchanged where the other image has 0 alpha, and the output alpha is set to a+b - a*b. When disabled the alpha channel is processed as any other channel. Option is disabled for operations where it does not apply or makes no difference.
R / AChannelsR	Boolean	On	Use red channel from A input(s).
G / AChannelsG	Boolean	On	Use green channel from A input(s).
B / AChannelsB	Boolean	On	Use blue channel from A input(s).
A / AChannelsA	Boolean	On	Use alpha channel from A input(s).
R / BChannelsR	Boolean	On	Use red channel from B input.
G / BChannelsG	Boolean	On	Use green channel from B input.
B / BChannelsB	Boolean	On	Use blue channel from B input.
A / BChannelsA	Boolean	On	Use alpha channel from B input.
R / OutputChannelsR	Boolean	On	Write red channel to output.
G / OutputChannelsG	Boolean	On	Write green channel to output.
B / OutputChannelsB	Boolean	On	Write blue channel to output.
A / OutputChannelsA	Boolean	On	Write alpha channel to output.
Invert Mask / maskInvert	Boolean	Off	When checked, the effect is fully applied where the mask is 0.
Mix / mix	Double	1	Mix factor between the original and the transformed image.